Discharge lamp and method of manufacture



Jan. 12, 1943. P. w. BLACKBURN 2,308,350

DISCHARGE LAMP AND METHOD 0F MANUFACTURE Filed 001.. 3l, 1959 INVENTOR 214/. namaak/v Y ATTORNEY Patented Jana 12, 1943 DISCHARGE LAMP AND METHOD F MANUFACTURE Philip W. Blackburn, East Orange, N. J., assigner to Westinghouse Electric & Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application October 31, 1939, Serial No. 302,123

p 4 Claims.

This invention relates to discharge lamps and the method of manufacture, and more particution of discharge lamps, and then the etching of the envelopes of such lamps as may have a sub-normal ultraviolet output, in order to increase the output to that desired.

A further object of my invention is the construction of ultraviolet generating discharge lamps by manufacturing in the usual way, seasoning, determining the ultraviolet output, and then differentially etching the envelopes of said thickness.

lamps to make them all generate the same in- Y tensity of ultraviolet radiations.

Other objects and advantages of the invention, relating to the particular arrangement and construction of the Various parts, will become apparent as the description proceeds.

Referring to the drawing illustrating my invention:

Figure 1 is a view of a lamp embodying my invention, partly in elevation and partly in longitudinal section.

Figure 2 is an enlarged fragmentary view of one end portion of a lamp, such as shown in Figure 1, a coating of wax or other protective means being shown applied to said end portion in order to avoid attack by Vetching fluid.

Figure 3 is a chart showing the ratio between glass thickness and percentage transmission of radiations.

Figure 4 is a diagrammatic View of apparatus which may be employed for etching lamps in accordance with my invention.

Referring to the drawing in detail, there is shown a discharge lamp II, comprising an enous material varies asa logarithmic function of the thickness. By decreasing the wall thickness, we can immediately increase the transmitted amount of the short wave length rays, or those in the ultraviolet portion of the spectrum.

Ultraviolet glass, as obtained from the manufacturer, varies in at least three dilerent ways. In the first place, the Wall thickness of the tubing or bulb cannot be held to close tolerances. In fact approximately a two to one variation may be expected in glass of this type. For instance, if we require a glass of .030" thickness, the spread on the material received will usually be from .020" to .040. In order to illustrate the effect of this, the curves I3 and I0 of Figure 3 are referred to. Both of these are shown on semilogarithmic paper with the ordinates on the log.

arithmic scale, representing the percentage transmission of radiations, and the abscissas, on the conventional scale, representing the wall Curve I3 shows a transmission of 2.5% at .020" thickness and curve I4 a transmission of 40%' at .020". These curves might apply to different wave lengths with a particular glas's, or to the same wave length for different lots of glass, or to different wave lengths for different lots of glass.

From these curves it will be seen that a variation in wall thickness will give a tremendous 'difference in output in lamps of normal manufacture. For example, with curve I3, if the thickness of the glass, initially .020", is cut in half, the

transmission increases from 21/2% to 15.6%. With a glass and wave length corresponding with the curve I 4, if the glass thickness is decreased from .020 to .010", the transmission, for radiation of that wave length, increases from 40% to about S21/2%. It is, therefore, desired to make up lamps with tubing as received, and then after determining the output by taking a reading, etch oi the required amount to make the output of each lamp as desired, so that the output of all the lamps is uniform.

In the second place, different lots of ultraviolet glass vary considerably in ultraviolet transmission even in the same wall thickness. For example, I'have seen glass supposedly of the same composition in which the transmission of a certain line, in the ultraviolet part of the spectrum, varied from 20% in a piece one millimeter thick to 50% in another piece one millimeter thick. I have also seen glass of supposedly the same approximate composition in which the transmission of another line, in the ultraviolet part of the spectrum, variedfrom as low as .01% in one piece one millimeter thick to as high as in another piece one millimeter thick. The only way such lamps could be made uniform in their ultraviolet output would be to etch the lower transmission glass down until its transmission had increased, in accordance with Figure 3, to agree with a lamp made of higher transmission glass.

In the third place, the solarization effect varies materially with different lots` of glass. That is, in a few hours of operation the glass will change materially in ultraviolet transmission. For example, some glasses solarize very little, perhaps 10%, and other glasses solarize more than 50% with regard to the 2537 angstrom line in the ultraviolet. To obtain uniform lamps under this condition, .it is necessary to season the lamps first to obtain their output, and then etch them to the desired extent. Y

- While in the above, I have given the three different characteristics which aiect the output of lamps, in actual operation it is necessary to contend with all three at all times. Therefore, to obtain uniformity, and in many cases to obtain suilicient output, it is necessary to reduce the thickness of the envelope walls after the lamps have been made, seasoned, and their output read.

If it is desired to obtain an extremely high output in the ultraviolet part of the spectrum, it is necessary to have the bulbs or tubing very thin, say .010" or .015" in wall thickness. It would be impossible to fabricate lamps or tubes with glass of such wall thickness. However, I propose to make them with heavier walls and then, after fabrication, etch the glass down to the proper wall4 thickness. They would the'n be strong enough, after having been once assembled, to be used for practical purposes.

Before proceeding to practice my invention, I completely finish the tube, as illustrated in Figure l except'that the central attenuated tubular portion I5 has glass of normal thickness, as indicated in full lines in Figure 2. At the ends of the tubular or attenuatedportion I5, are chambers I6 and I1 containing electrodes I8 and I9. These electrodes may be such as disclosed in the James application Serial No. 734,620, led July ll, 1934, and owned by the assignee of the present application. The lamp may also be constructed otherwise as disclosed ,in said application, and that is, the ionizable medium in the envelope may be a rare gaseous filling, such as a mixture of 60% neon and 40% argon, to which is added a small quantity of mercury iu order to increase the intensity of the ultraviolet radiation, especially adjacent the resonance line 2537 A. U. The pressure of the medium is desirably from 5 to 20 mm., or about 8 mm.

The envelope may be exhausted and gas-lled ln the conventional manner, and sealed-olf at the tip, indicated at 2|. The lamp is desirably provided with contact caps 22 and 23, applied to the ends, which caps are in electrical connection l with the respective electrodes I8 and I9.

lamp becomes 'approximately constant, a read- Suppose, for example, that We are interested in'a glass and ultraviolet portion of the spectrum corresponding with the curve I3 in Figure 3, and that the reading showed that the transmission of that portion of the spectrum was 21/2%, and that in order to get the desired output, it was necessary to have a transmission of 10%. A reference to the curve I3 will show that the thickness of the glass, to obtain the 10% transmission, would have to be reduced from the original thickness of .020" to about .0125, or a reduction in the thickness of the glass to flve-eighths of that which' it had originally. From knowledge of the speed of etching of the fuid which is used for the purpose,'we then know exactly how long to leave the envelope in said etching fluid to give it the desired transmission characteristics.

Assuming then that we have made and read a lamp such as shown in Figure 2, we then apply a coating of paraiiine or other protective wax over the end chambers and contact caps I8 and I1, 22 and 23, as illustrated most clearly at 24. The lamp or lamps, is or are, then mounted on a rack 25 and suspended by means of a rod 26 from an oscillating member 21 in an etching fluid bath 28, which bath is desirably 60% hydrouoric acid. The oscillating rod 2 1 is pivotally molmted on a bracket 29, as indicated at 3l, and

pivotally carries the rod 28, as indicated at 32. 'I'he oscillation of the rack 25 in the bath 28, is effected in any desired manner, as by means of a rod 33, pivotally mounted on the other end of the rod 21, as indicated at 34, and connected to a crank arm 35, as indicated at 36. Means, such as an electric motor 31, is provided for operating the crank arm 35, as through reduction gears in a gear box 38.

After the rack of lamps I I have been oscillated in the etching fluid. 28 for the desired period of time, said rack is removed and transferred to a tank of water 39, in which it is preferably oscillated thoroughly until freed of etching fluid. While in the tank 39, it may be pivotally suspended from the oscillating member 21, as indicated at 4I. Water is desirably Acirculated through the tank during the washing period, through inlet and outlet pipes 42 and 43, respectively.

After removal from the washing water 33, the lamps, which have had the thickness of the attenuated portion I5 reduced to that shown in dotted lines in Figure 2, while the end chambers are unaffected because of the protective coatings 24, may be freed of these coatings and the lamps are then ready for use. v

From the foregoing disclosure, it will be seen that I have devised a discharge lamp particularly adapted for eiciently generating ultraviolet radiations, and especially those in the neighborhood of the mercury lines between 2530 and 2540 A. U., said generator having its output definitely predetermined, assuming constant operating conditions, by having the thickness of the glass adjusted for that output. I have also devised a desirable method for manufacturing such lamps. Although a preferred embodiment of my invention has been disclosed, it will be understood that modifications may be made within the spirit and scope of the appended claims.

' I claim: K

1. The method of standardizing the output of ultraviolet lamps each having a vitreous envelope, comprising constructing in the usual way, seasoning, reading the ultraviolet output, and etching, if said output is under that desired, to reduce v 2,808,350Y the wail thickness of said envelope to such an desired, for the length of time necessary to reextent that the output rises to standard.

2. The method oi standardizing the output of ultraviolet lamps each having a vitreous envelope, comprising constructing in the usual way, seasoning, reading theultraviolet output, and immersing in hydroiluoric acidfif said output is under that desired', for the length ofgtime necessary to reduce the wall thiess of said envelope to suhh an extent that the output rises to standard.

, 3. The method of standardizing the output of ultraviolet lamps each having a vitreous envelope,

duce the wail thickness of said envelope to such an extent that the output rises to standard.

4. 'I'he method of standardizing the output of ultra-violet lamps each of which has an elongated vitreous envelope terminating in end chambers provided with contact caps, comprising seasoning, reading the ultra-violet output, coating the end chambers and caps with protective wax, and immersing and agitating in hydroiuoric acid for a length of time necessary to reduce the thickness between end chambers to that necessary'to give the desired standard output under normal operating conditions.

PHILIP W. BLACEURN. 

